1. Field of the Invention
The field of art to which the claimed invention pertains is solid-bed adsorptive separation. More specifically, the invention relates to a process for the separation of polar organic compounds containing sulfur, oxygen or nitrogen atoms from a feed mixture comprising naphtha and such compounds, which process employs a solid adsorbent which selectively removes the compounds from the feed mixture thereby producing a naphtha raffinate stream having a reduced content of such compounds.
2. Description of the Prior Art
It is well-known in the separation art that certain crystalline aluminosilicates can be ued to separate hydrocarbon species from mixtures thereof. The separation of normal paraffins from branched chain paraffins for example can be accomplished by using a type A zeolite which has pore openings from about 3 to about 5 angstroms. Such a separation process is disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the zeolitic adsorbent, while excluding the larger or branched chain molecules.
U.S. Pat. Nos. 3,265,750 and 3,510,423, for example, disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
In addition to separating hydrocarbon types, the type X or type Y zeolites have also been employed in processes to separate individual hydrocarbon isomers. In the process described in U.S. Pat. No. 3,114,782, for example, a particular zeolite is used as an adsorbent to separate alkyl-trisubstituted benzene; and in U.S. Pat. No. 3,668,267 a particular zeolite is used to separate specific alkyl-substituted naphthalenes. In processes described in U.S. Pat. Nos. 3,558,732 and 3,686,342 adsorbents comprising particular zeolites are used to separate para-xylene from feed mixtures comprising para-xylene and at least one other xylene isomer by selectively adsorbing para-xylene over the other xylene isomers.
In the process described in U.S. Pat. No. 3,917,734 issued to A. J. deRosset, ethylbenzene is recovered in high purity from a feed mixture comprising ethylbenzene and xylene isomers. The process basically comprises contacting the feed mixture with an adsorbent comprising calcium exchanged type X or type Y zeolites, selectively adsorbing the xylene isomers, and thereafter recovering ethylbenzene as a raffinate component. The adsorbent employed is thus all-xylene selective rather than para-xylene selective as are the adsorbents used in the para-xylene separation process. The adsorbed xylenes may then be recovered, in one embodiment, by contacting the adsorbent with a desorbent material, preferably comprising toluene, thereby desorbing the xylenes and then withdrawing the desorbed xylenes from the adsorbent. In another embodiment the adsorption and desorption are done continuously in a simulated moving-bed countercurrent flow system, the operating principles and sequence of which are described in U.S. Pat. No. 2,985,589.
Solvent refined coal naphtha, a naphtha cut of a coal liquefaction product, could prove to be a major addition to the motor fuel gasoline pool. One drawback is that it contains considerable quantities of "sour" components; mainly polar organic compounds comprising oxygenates, nitrogenates and sulfur bearing compounds. If the amount of these components could be substantially reduced, the sweetened product could then be blended to make gasoline. I have discovered a process which achieves such a reduction by making novel use of the principles of operation of the above discussed process and employing a crystalline aluminosilicate selective for such "sour" components.